A light-receiving device of one type includes a plurality of serial connections, each including a quenching resistor and an avalanche photodiode (APD) connected in parallel. The light-receiving device measures the number of incident photons using the APDs. The light-receiving device is typically referred to as “SiPM (Silicon Photomultiplier)” since the APDs are formed of silicon (Si).
It is expected to employ the light-receiving device having the APDs in an automatic operation (driving) system so that light reflected by an object can be measured for measuring a distance to the object. The APD formed of silicon, however, has low sensitivity to long-wavelength light. On the other hand, the cost of the light-receiving device would increase if the light-receiving device is formed of a semiconductor material so as to detect the long-wavelength light. It is desirable to provide a light-receiving device capable of detecting long-wavelength light with high sensitivity and lower cost.